Added comment about stream ids.
Merge github.com:wlanslovenija/datastream
More comments.
Datapoints can now be properly iterated. Fixes #11
Removed callback. Fixes #7
Don't round timestamps and don't mind gaps.
Implemented derive_from descriptors.
Merge github.com:wlanslovenija/datastream
Added test for chained derived streams.
Handle source streams with lower granularities.